On the Correlation between Hot Jupiters and Stellar Clustering: High-eccentricity Migration Induced by Stellar Flybys

TL;DR

This paper proposes a new formation scenario for hot Jupiters involving stellar flybys that excite outer companions' eccentricity, leading to high-e migration of inner planets, potentially explaining observed correlations with stellar clustering.

Contribution

It introduces the 'Flyby Induced High-e Migration' scenario, combining analytical and numerical methods to estimate hot Jupiter occurrence rates influenced by stellar flybys.

Findings

Flyby events can significantly increase hot Jupiter formation rates.

The scenario explains the correlation between stellar clustering and hot Jupiter occurrence.

Results depend on cluster density, lifetime, and planetary system architecture.

Abstract

A recent observational study suggests that the occurrence of hot Jupiters (HJs) around solar-type stars is correlated with stellar clustering. We study a new scenario for HJ formation, called "Flyby Induced High-e Migration", that may help explain this correlation. In this scenario, stellar flybys excite the eccentricity and inclination of an outer companion (giant planet, brown dwarf, or low-mass star) at large distance (10-300 au), which then triggers high-e migration of an inner cold Jupiter (at a few astronomical units) through the combined effects of von Zeipel-Lidov-Kozai (ZLK) eccentricity oscillation and tidal dissipation. Using semianalytical calculations of the effective ZLK inclination window, together with numerical simulations of stellar flybys, we obtain the analytic estimate for the HJ occurrence rate in this formation scenario. We find that this "flyby induced high-e migration" could account for a significant fraction of the observed HJ population, although the result depends on several uncertain parameters, including the density and lifetime of birth stellar clusters, and the occurrence rate of the "cold Jupiter + outer companion" systems.